This invention relates to dental materials with an extendable work time. More specifically, the dental materials have a relatively fast initial set phase and a subsequent extended flexible phase working time. Preferably, the dental materials are used as provisional oral prosthetic devices such as inlays, onlays, veneers, temporary crowns, permanent crowns, and bridges.
Currently available dental materials for the fabrication of provisional restoratives include polymerizable resins, which have replaced the use of metal shells and polycarbonate temporary crowns. Resin-based crowns can be made available in different shades that can be matched to the patient""s dentition. Two-part resin formulations are typically used wherein the resin constituents are separate from the initiator system. The resin constituents are typically free radically polymerizable monomers (e.g., acrylates, methacrylates, and acrylamides). The initiator system typically includes reducing agents, such as tertiary amines, and oxidizing agents, such as peroxides, as accelerators or activators for free radical polymerization and control of the rate of polymerization.
It is desirable to control the rate of polymerization such that the dental material has a relatively rapid initial set phase time during which time a specific hardness is attained without locking into the undercuts produced during tooth preparation, followed by an extended flexible phase work time. During this flexible phase the dental material can be removed from the mouth to allow the dental practitioner time to modify, trim, and adjust the dental material for a custom fit onto the prepared tooth. Modification and adjustment of the dental material during the extended flexible phase is desirable in order to provide a more custom fit of the provisional restorative in the mouth of the patient. Additionally, heat generated by the exothermic polymerization is controlled by removal of the dental material from the intra-oral environment. This also avoids damage to oral tissues and consequently provides more comfort for the patient. Before final placement in the mouth and cementing in place, the restorative is completely hardened by conventional means commonly known for free radical polymerization.
A typical procedure for making a provisional dental restorative involves the following steps. Initially, an alginate impression is taken before preparing the teeth. The impression is rinsed, set aside, and wrapped in a moist paper towel. The teeth are then prepared and the correct shade of acrylic powder is selected to match the natural teeth. An acrylic liquid resin and the acrylic polymeric powder, one of which includes a reducing agent and the other of which includes an oxidizing agent, are mixed together and placed in the impression. The impression is placed aside until the composition thickens and forms a dull appearance (approximately 45-60 seconds). Meanwhile, the prepared teeth and surrounding tissue are coated with a petroleum jelly, which ensures easy removal of the acrylic temporary from the preparation and protects the teeth and tissue from irritation by the acrylic mixture. The impression with the acrylic mixture is seated in the mouth and held in place for a sufficient time to allow it to harden to a removable state. Mixing through this stage is the initial set phase time. The acrylic material is removed from the impression and gross excess acrylic is trimmed. The acrylic material is placed in and out of the mouth while the acrylic material is in a rubbery state. This is the extended flexible phase work time. The acrylic material is removed from the mouth and set aside until the acrylic is fully cured. The fit of the acrylic restorative is checked and adapted to fit, if necessary. Excess acrylic is trimmed with an acrylic bur or stone and polished to a smooth finish. The acrylic temporary is then cemented into place.
The important time during the preparation of a restorative occurs after the resin, initiator, and reducing agent are mixed together. It is important that hardening occurs initially rapidly (during the initial set phase time), but then slows to allow a dental practitioner to place, remove, and trim the restorative material (during the extended flexible phase work time) before it continues to harden to such a state as to become unworkable. There is a need for dental materials that provide reasonable initial set phase times and flexible phase work times that are more readily controllable than conventional materials.
The present invention provides a dental material useful for the fabrication of dental restoratives. Such a dental material includes a resin system and a first initiator system. Preferably, it also includes a filler system, and more preferably, a second initiator system. Once the components are combined to initiate a reaction, the time period during which the resultant composition solidifies to a partially hardened state is referred to herein as the initial set phase time. The partially hardened material at this point is firm enough to be removed from the mouth without being permanently deformed, but not so rigid that the solidified impression locks into undercuts and becomes too hard and brittle to be trimmed. The material then has an extended flexible phase work time sufficient for the dental practitioner to place, remove, and trim the dental material before it continues to harden to such a state as to become unworkable. The dental restorative can be further hardened to a rigid phase extra-orally.
In one embodiment, the dental material includes a hardenable resin system and a first initiator system capable of hardening the hardenable resin. Optionally and preferably, the dental material also includes a filler system and a second initiator system. Preferably, the hardenable resin system and the first initiator system are selected such that when combined the resultant composition has an initial set phase time of less than about 180 seconds at room temperature, and an extended flexible phase working time of greater than about 85 seconds at room temperature.
The first initiator system preferably includes at least one reducing agent and at least one oxidizing agent. Preferably, the oxidizing agent is a peroxide compound and the reducing agent is a tertiary aromatic amine, a mercaptan, or combinations thereof. Typically and preferably, the dental material is provided in at least two parts, wherein at least one part includes at least one reducing agent and at least one other part includes at least one oxidizing agent, which together form the first initiator system.
In a preferred embodiment, the dental material includes a hardenable resin system and a first initiator system capable of hardening the hardenable resin, wherein the first initiator system includes at least one polymerizable tertiary aromatic amine. Preferably, the polymerizable tertiary aromatic amine is selected from the group of bis-N,N-[2-(2-methacryloloxyethylaminocarbonyloxy)ethyl]-p-toluidine, bis-N,N-(2-methacryloloxyethyl)-p-toluidine, 4-[2(2-acrylamido-2-methylpropionyloxy)ethyl)-N,N-dimethlyaniline, bis-N,N-[2-(2-acrylamido-2-methylpropionyloxy)ethyl]-p-toluidine, and mixtures thereof.
In another preferred embodiment, the dental material includes a hardenable resin system and a first initiator system capable of hardening the hardenable resin, wherein the first initiator system includes at least two peroxide oxidizing agents.
In yet another preferred embodiment, the dental material includes a hardenable resin system and a first initiator system capable of hardening the hardenable resin, wherein the first initiator system includes at least two reducing agents, at least one of which is a mercaptan.
In still another preferred embodiment, the dental material is suitable for use as a provisional restorative and includes a hardenable resin system and a first initiator system capable of hardening the hardenable resin, wherein the first initiator system includes at least two tertiary aromatic amine reducing agents.
The present invention also provides a kit for preparation of a dental restorative. The kit includes: a first container including at least one reducing agent; a second container including at least one oxidizing agent; and at least a portion of a hardenable resin system in at least one of the containers; wherein the hardenable resin system, reducing agent, and oxidizing agent are selected such that when combined the resultant composition has an initial set phase time of less than about 180 seconds at room temperature, and an extended flexible phase working time of greater than about 85 seconds at room temperature.
In another embodiment, the kit includes: a first container including at least one oxidizing agent; a second container including at least one polymerizable tertiary aromatic amine reducing agent; and a hardenable resin system in at least one of the containers.
In yet another embodiment, the kit includes: a first container including at least two peroxide oxidizing agents; a second container including at least one reducing agent; and a hardenable resin system in at least one of the containers.
In still another embodiment, the kit includes: a first container including at least one oxidizing agent; a second container including at least two reducing agents, at least one of which is a mercaptan; and a hardenable resin system in at least one of the containers.
The present invention also provides a method for preparing a dental restorative. The method involves: making an impression of at least one tooth; filling the impression with a hardenable composition comprising a hardenable resin system and a first initiator system, wherein the hardenable resin system and the first initiator system are selected such that when combined the resultant composition has an initial set phase time of less than about 180 seconds at room temperature, and an extended flexible phase working time of greater than about 85 seconds at room temperature; placing the impression over at least one tooth to partially harden the hardenable composition; removing the impression and partially hardened composition and removing excess hardened material to form a dental restorative; and allowing the dental restorative to further harden.
The dental materials of the present invention include a hardenable resin. As used herein, xe2x80x9charden,xe2x80x9d xe2x80x9chardening,xe2x80x9d and xe2x80x9chardenablexe2x80x9d is descriptive of a resin that can be polymerized and/or crosslinked.
xe2x80x9cDental materialxe2x80x9d refers to a combination of components that upon reaction form a material that is suitable for use in a patient""s dentition. Herein, dental material refers to the unreacted components (e.g., various combinations of hardenable resin, initiator systems, etc.) as well as the reacted components.
xe2x80x9cInitial set phase timexe2x80x9d is the time period, as measured in seconds, during which time the dental material hardens to a hardness of 20 (i.e., T20), as determined by measuring with a Shore A Durometer (The Shore Instrument and Manufacturing Co., New York, N.Y.), at room temperature. Typically, the initial set phase time starts with mixing the oxidizing agent, reducing agent, and resin.
xe2x80x9cExtended flexible phase timexe2x80x9d is the time period wherein the dental material that has obtained a hardness of 20 on the Shore A Durometer is allowed to harden to a hardness of no greater than 80 (i.e., T80), as determined by measuring with a Shore A Durometer, at room temperature. The extended flexible phase time, as measured in seconds, is obtained by subtracting T20 from T80.
xe2x80x9cRestorativexe2x80x9d refers to an oral prosthetic device, such as an inlay, onlay, a veneer, a single unit crown, a splint, a crown lining material for prefabricated crowns, an implant, or multiple unit bridges. xe2x80x9cProvisional Restorativexe2x80x9d is a temporary placement intended for eventual removal and replacement by a more long term or permanent device. Typically, a provisional restorative is intended to be in the intra-oral environment for no greater than about a year, preferably for no greater than about 6 months, and more preferably no greater than about 30 days.